A cross-sectional view of a conventional fastener is shown in FIG. 1. The figure illustrates how the fastener secures a stack of documents, with two side sheet retainers stemming from the body of the base, and a keeper. The keeper consists of a strip of metal with two longitudinal raised strips along both longitudinal edges to increase the stiffness of the keeper, and two sliding locks. Two side sheet retainers pass through the holes in the paper and the two side perforations of the keeper sit on the top of the paper file. The purpose of the locks is to hold the ends of the sheet retainers down into the groove between the raised strips of the keeper. The locks can be moved over the entire length of the keeper and be held at any position due to resilience of the metal sheet retainers. Both ends of the keeper are either slightly wider or have a depressed notch so that the locks may not escape from the keeper.
When the space between two side perforations of the keeper is eight and a half inches, the fastener leaves the center portion of the paper loose, particularly when the volume of the paper increases. Also, the locks tend to slide away from the desired location on the sheet retainers due to lack of resilience of the sheet retainers. In prior fasteners utilizing only two side sheet retainers on the base, when the locks are not in the desired position due to lack of resilience (this is most often the case), the ends of the sheet retainers became loose, resulting in insecure binding. This is more obvious as the thickness of paper increases and/or the distance between the side perforations increase.